Super Cooler for a Heat Producting Device

ABSTRACT

A super cooler device including a thermo electric cooler on a digital micro mirror device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 10/794,258, filed Mar. 4, 2004, which is a continuation of U.S. application Ser. No. 10/375,165, filed Feb. 25, 2003, now U.S. Pat. No. 6,775,991, which is a continuation of U.S. application Ser. No. 10/128,774, filed Apr. 22, 2002, now U.S. Pat. No. 6,523,353, which is a divisional of U.S. application Ser. No. 09/780,025, filed Feb. 9, 2001, now U.S. Pat. No. 6,430,934, which claims the benefit of U.S. provisional application Ser. No. 60/181,530 filed Feb. 10, 2000.

SUMMARY

The present application relates to cooling of a heat producing device, using a thermoelectric cooler arranged as a super cooler. More specifically, the present application teaches cooling of a device, such as a digital mirror device, which requires a specified temperature gradient across the device, using a supercooled element.

BACKGROUND

Electronic devices often have specified cooling requirements. One device that has specific cooling requirements is a digital micromirror device (“DMD”) available from Texas Instruments (“TI”). The manufacturer of this device has specified a maximum overall temperature for the device and also a specified maximum temperature gradient between the front and rear faces of the device during operation.

For example, the temperature of the specific DMD used in this application needs to be kept below 55° C., however, in this application it is desirable to keep the device at or below ambient. This may allow operation in an ambient environment up to 55° C., such as may be encountered in a stage theater or studio environment. The temperature differential between the front and rear of the DMD cannot exceed 15°. Besides the heat from the operation of the DMD itself, large amounts of heat from a high intensity light source must be dissipated.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects will now be described in detail with reference to the accompanying, wherein:

FIG. 1 shows an exploded diagram of the parts making up the supercooler assembly;

FIG. 2 shows the rear of the DMD and parts which are assembled to the DMD;

FIG. 3 shows a circuit for driving a thermoelectric cooler; and

FIG. 4 shows a flowchart of operation.

DETAILED DESCRIPTION

According to the present system, a “supercooler” device, is used to monitor and control the temperature of a device which can control light on a pixel-by-pixel basis, e.g. a digital mirror device (DMD).

The mechanical structure of the supercooling assembly is shown in FIG. 1. The pixel element is a DMD 99, which forms part of a DMD assembly 100. As shown, a thermal connection 105 to the DMD 99 is provided. A lighting projector 155 projects light 156 on the front surface 157 thereof.

A cold plate 120 is assembled to a mounting bracket 110 in a manner which allows minimal thermal transfer between the two components. The DMD is attached directly to the cold plate 120, hereby allowing maximum thermal transfer between the DMD and cold plate 120, but minimal thermal transfer to the mounting bracket 110. The rear surface of the cold plate 120 is directly connected to one side of the thermoelectric device 130, and the other side of the thermoelectric device is connected to a heat sink/fan assembly 140.

Insulating foam gaskets are fitted around the DMD rear stud, the cold plate, and the thermoelectric device in order to isolate them from the outside ambient air. This improves the efficiency of the cooling system by eliminating the effects of condensation and properly controlling the flow of heat from the DMD to the cold plate, through the thermoelectric device, and into the heat sink/fan assembly.

The thermoelectric cooler element 130 operates as conventional to produce one cold side 131 and one hot side 132. The hot side is coupled to the heat sink/fan assembly 140 to dissipate the heat. In a preferred mode, the heat sink/fan assembly is columnar is shape, with a substantially square cross section. This facilitates using a square shaped fan housing 142. The square shaped fan unit allows the maximum use of the space for a fan, whose blades usually follow a round shape. Any type of cooling fan, however can be used.

The DMD assembly 100 has an extending rear stud 105 which is covered with thermal grease. This stud extends though a hole 112 in the bracket assembly 110.

The plate 120 is actively cooled, and hence becomes a “cold plate”. The active cooling keeps the metal plate at a cooled temperature, and the thermal characteristics of the plate material allow the heat flowing into the plate from the DMD to be evenly distributed throughout the entire plate. The plate is preferably about ¼″ to ⅜″ in thickness, and of comparable outer size to the thermal contact area of the thermoelectric cooler element 130. This allows the localized and concentrated heat at the rear stud of the DMD to be evenly dissipated through the cold plate and then efficiently transferred through the full surface area of the thermoelectric cooler element. As shown, the assembly employs thermal insulation techniques such as fiber/plastic sleeves and washers in the mounting of components, in order to prevent heat transfer via mounting screws etc. Since this heat transfer could be uncontrolled, it could otherwise reduce the cooling efficiency.

The front of the DMD is shown in FIG. 2. Temperature sensor 200 is mounted to have a fast response to temperature changes. A second temperature sensor 122 is mounted to the cold plate 120 and effectively measures the temperature of the rear of the DMD 99. This second temperature sensor 122 therefore monitors the back temperature.

The hot side 132 of the thermoelectric cooler is coupled to a heat sink assembly 130. The heat sink assembly 140 includes a heat sink element 140. As shown, the device has fins and a top-located cooling fan 142.

A block diagram of the control system is shown in FIG. 3. Controller 300 operates in a closed loop mode to maintain a desired temperature differential across the sensors 122,200.

One important feature of the present application is that the thermoelectric cooler is controlled to maintain the temperature of the DMD at the desired limits. These limits are set at a target of 16° C. on the front, and a differential no greater than 15° between front and rear. The thermoelectric cooler is controlled using very low frequency or filtered pulse width modulation. In a first embodiment, the controlling micro controller 300 produces an output 302, e.g., digital or analog. This drives a pulse width modulator 304. The output of the pulse width modulator is a square wave 306 or a signal close to a square wave, with sufficient amplitude and power to produce the desired level of cooling down the thermoelectric cooler. The square wave is coupled to an LC filter 308 which has a time constant effective to smooth the 20 KHz switching frequency. The output to the thermoelectric cooler is therefore a DC signal. This drives the thermoelectric cooler 130 and causes it to produce a cooling output. In a second embodiment, the LC filter is removed and the TEC is driven directly by the square wave 306 at a lower frequency, e.g. 1 Hz.

The microcontroller operates according to the flowchart of FIG. 4. Step 400 determines if the temperature of the first temperature sensor T1 is greater than 16°. If so, the output to the TEC remains “on”, resulting in further cooling. When the temperature falls below 16°, the drive to the TEC is switched off. The sample period is approximately ½ second between samples.

At 410, the system checks temperature of the first sensor (T1) and of the second sensor (T2) to determine if the differential is greater than 15°. If so, the output is switched “on”. Step 420 indicates a limit alarm, which represents the time of increase if the rate of change continues. If the rate of change continues to increase, as detected at step 420, a fault is declared at step 425. This fault can cause, for example, the entire unit to be shut off, to reduce the power and prevent permanent damage.

Other embodiments are contemplated. 

1. A system, comprising: an electrically controllable device that is electrically controllable to control light on a pixel by pixel basis; and a cooling device, connected thermally to said electrically controllable device, and operating to actively cool said electrically controllable device, where said operating provides a first nonzero amount of cooling based on detecting a need for providing a first cooling amount, and where said operating provides a second nonzero amount of cooling, based on detecting a need for providing a second nonzero cooling amount, wherein said first nonzero cooling amount is different then said second nonzero cooling amount.
 2. A system as in claim 1, wherein said need for a cooling amount depends on a temperature differential between a front surface and back surface of said electrically controllable device.
 3. A system as in claim 1, wherein said electrically controllable device is a digital mirror device.
 4. A system as in claim 1, wherein said cooling device carries out said amount of cooling and said second cooling amount using pulse width modulation of an electrically controllable cooling device.
 5. A system as in claim 1, wherein said cooling device turns on for a first time and turns off for a second time to change said amount of cooling.
 6. A system as in claim 1, wherein said electrically controllable device is thermally connected to a thermally conducting plate, and said cooling device is thermally coupled to said thermally conducting plate.
 7. A device as in claim 6, wherein a portion of said thermally conducting device extends through said plate.
 8. A device as in claim 1, wherein said cooling device includes a thermoelectric cooler.
 9. A system, comprising: an electrically controllable device that is electrically controllable to control light on a pixel by pixel basis; a cooling device, thermally coupled to said electrically controllable device, and cooling said electrically controllable device; and a controller for said cooling device, controlling said cooling device based on a temperature differential between a front surface of said electrically controllable device and a rear surface of said electronically controllable device.
 10. A system as in claim 9, wherein said controller includes a temperature sensor on a front surface of said electrically controllable device and a temperature sensor on a rear surface of said electrically controllable device.
 11. A system as in claim 9, wherein said controller controls an amount of cooling per unit time between multiple cooling nonzero values.
 12. A system as in claim 11, wherein said amount of cooling per unit time is carried out based on pulse width modulation.
 13. A system as in claim 11, wherein said cooling device includes a thermoelectric cooler.
 14. A system as in claim 9, wherein said electrically controllable device is attached to a thermally conductive plate, and wherein said cooling device is connected to said plate and not to said device.
 15. A method, comprising: operating an electrically controllable device that is electrically controllable to control light on a pixel by pixel basis, said operating comprising changing an applied light beam to create a light output; cooling said electrically controllable device, and cooling said electrically controllable device; and controlling an amount of said cooling device based on a temperature differential between a front surface of said electrically controllable device and a rear surface of said electronically controllable device.
 16. A method as in claim 15, wherein said controlling comprises controlling an amount of cooling per unit time between multiple nonzero cooling values.
 17. A method as in claim 16, wherein said amount of cooling per unit time is carried out based on pulse width modulation.
 18. A method as in claim 15, wherein said cooling uses a thermoelectric cooling.
 19. A method, comprising: operating an electrically controllable device that is electrically controllable to control light on a pixel by pixel basis, said operating comprising changing an applied light beam to create a light output; and controlling cooling of said said electrically controllable device, wherein said controlling provides a first nonzero amount of cooling based on detecting a need for providing a first cooling amount, and where said operating provides a second nonzero amount of cooling, based on detecting a need for providing a second nonzero cooling amount, wherein said first nonzero cooling amount is different then said second nonzero cooling amount.
 20. A method as in claim 19, wherein said need for a cooling amount depends on a temperature differential between a front surface and back surface of said electrically controllable device.
 21. A method as in claim 19, wherein said cooling turns on for a first time and turns off for a second time to change said amount of cooling.
 22. A method as in claim 19, wherein said electrically controllable device is thermally connected to a thermally conducting plate, and said cooling device is thermally coupled to said thermally conducting plate.
 23. A system, comprising: an electrically controllable device that is electrically controllable to control light on a pixel by pixel basis; and a cooling device, connected thermally to said electrically controllable device, and operating to actively cool said electrically controllable device; and a controller, controlling an amount of cooling by said cooling device wherein said controller controls an amount of cooling per unit time between multiple cooling nonzero values. 